Drilling bit for drilling while running casing

ABSTRACT

A drill bit for drilling casing in a well bore. The drill bit is constructed from a combination of relatively soft and relatively hard materials. The proportions of the materials are selected such that the drill bit provides suitable cutting and boring of the well bore while being able to be drilled through by a subsequent drill bit. Methods of applying hard materials to a soft material body are provided.

This application is a National Stage of International Application No.PCT/GB00/04936, filed Dec. 21, 2000, which claims priority to GreatBritain patent application no. 9930287.9, filed Dec. 22, 1999, and GreatBritain patent application no. 0018309.5, filed Jul. 27, 2000.

The present invention relates to drilling tools as are typically usedfor drilling well bores.

Conventionally, when drilling a well bore of the type used in oil or gasproduction, a string of drill pipe having a drill bit on the lower endthereof is advanced into the ground. As the drill is advanced into theground it encounters different rock formations, some of which may beunstable. To minimise problems which may be incurred by running thedrill bit from one formation to another, it is common practice to runthe drill bit to a predetermined depth, and then remove or “trip” thedrill string from the bore. Structural casing, typically made of heavysteel piping, is then lowered into the bore and cemented in place whenset. The casing acts as a lining within the bore, and prevents collapseof the newly drilled bore or contamination of the oil or gas reservoir.

As a consequences of having to carry out the above procedure, the costand time taken to drill a bore is increased as it is necessary toperform a number of trips down the well. It will be appreciated that atthe considerable depths reached during oil and gas production the timetaken to implement complex retrieval procedures to recover the drillstring can be very long, and accordingly the beginning of profitableproduction can be greatly delayed.

An attempt has been made to mitigate this problem with the introductionof a procedure known as “drilling with casing”. This procedure relies onthe attachment of a drill bit to the actual casing string, so that thedrill bit functions not only to drill the earth formation, but also toguide the casing into the well bore. This is advantageous as the casingis pulled into the bore by the drill bit, and therefore negates therequirement of having to retrieve the drill string and drill bit afterreaching a target depth to allow cementing.

While this procedure greatly increases the efficiency of the drillingprocedure, a further problem is encountered when the casing is cementedupon reaching the desired depth. The advantage of drilling with casingis that the drill bit does not have to be retrieved from the well bore.However as a result, should drilling to a greater depth be requiredafter cementing the casing, the subsequent drill bit has to pass throughthe previous bit in order to advance. This is extremely difficult asdrill bits are required to remove hard rock material and are accordinglyvery resistant and robust structures typically manufactured frommaterials such as Tungsten Carbide or steel. Attempting to drill throughan old drill bit may result in damaging the new drill bit, adverselyaffecting the efficiency of any further drilling. Consequently, thedamaged drill bit would have to be retrieved from the bore and replaced,and the time and cost advantage gained by using the drilling with casingprocedure would be lost.

It would therefore be a distinct advantage to provide a drill bit foruse during drilling with casing which can drill rock and earthformations but which can also be drilled through by another drill bit.The provision of a drill bit which allows the passage of a subsequentdrill bit through it, would reduce the number of trips into a well borerequired during a normal drilling procedure and minimise the risk ofdamaging any further drill bits introduced into the bore.

In our prior Patent Application PCT/GB99/01816 we have suggested thatthe drill bit has hard drilling material that may be moved away from theremaining body of the drill shoe prior to subsequent drilling through ofthe drill bit. We have also proposed EP0815342, a drill bit or shoehaving hard drilling material placed only on the drill shoe or bit atthe peripheral circumference thereof, and specifically only at the sidesof the drill bit or shoe where the diameter is greater than the internaldiameter of the casing. The present invention is distinguished from bothof these teachings in that it provides for a drill shoe or bit that hashard material within the area below the internal boundaries of thecasing, and does not require moving parts to be displaced beforesubsequent drilling through can be commenced.

It is an object of the present invention to provide a drill bit for usein a well bore which can drill earth and rock formations and guide acasing string into a well bore simultaneously.

It is a further object of the present invention to provide a drill bitfor use in a well bore which is constructed from a material which allowsa second drill bit to drill through it.

It is a yet further object of the present invention to provide a drillbit for use in a well bore which allows a second drill bit to drillthrough it, such that the second drill bit is not damaged and canprogress beyond the point reached by the original drill bit within thewell bore.

According to a first aspect of the present invention there is provided adrill bit for drilling with casing in a well bore, said drill bit beingconstructed from a combination of a relatively soft material and arelatively hard material, wherein the hard material is suitable forcutting earth or rock, and wherein the combination of materials is insuch proportion and in such arrangement to allow a subsequent furtherdrill bit to drill through it.

Preferably the drill bit is substantially constructed from therelatively soft material, wherein the relatively soft material isadapted to be drilled through with a standard earth drill bit.

Preferably the drill bit is formed with a body having or beingassociated with a nose portion upon which are cutting members, whereinthe body is made substantially from the relatively soft material and atleast the leading edge or cutting surface of each cutting member is madefrom the hard material.

Preferably the hard wearing material is a hard material such as tungstencarbide or a superhard material such as diamond composite or cubic boronnitride although any other suitable material may be used.

Preferably the soft, drillable material is aluminium. Alternatively thesoft drillable material is copper or brass alloy, although any othersuitable material could be used.

There may be a plurality of soft materials and there may be a pluralityof hard materials.

In one possible embodiment the nose is directly coated with the hardwearing material.

Optionally the coating is a continuous layer or film that covers thesurface of the nose.

Alternatively the coating is non-continuous, such that the nose isafforded areas which are not coated by the hard wearing material,wherein upon rotation of the drill bit the cumulative effect of thecoated areas gives complete circumferential coverage of the dimensionsof the drilled hole.

Alternatively the coating may be applied to an intermediate which isamenable to the nose of the drill bit.

Preferably the intermediate is nickel.

The intermediate may be attached to the nose prior to coating with thehard wearing material. Optionally the intermediate may be coated withthe hard wearing material prior to attachment to the nose.

In a second embodiment the hard wearing material is applied to the nosein the form of preformed elements wherein the cumulative effect of saidpreformed elements is to cover the surface of the nose and so act as acoating thereof.

The preformed elements may be chips or fragments of the hard material.

The preformed elements of the hard material may be directly applied tothe nose.

Alternatively the preformed elements of hard material are applied to thenose following the application of an amenable intermediate material tothe nose or the preformed elements.

Preferably the amenable intermediate material is nickel substrate.

The preformed elements may be attached to the nose by standardtechniques such as brazing, welding or shrink fitting.

Optionally the preformed elements have a re-enforced structure to aiddrilling of hard formations. Where the preformed elements have are-enforced structure, preferably the preformed elements arepre-weakened prior to attachment to the nose in order to allow fractureof the preformed elements upon drilling.

Preferably the drill bit may also comprise a plurality of flow ports toallow fluid bypass and lubrication of the bit.

Preferably the drill bit also comprises a stabiliser or centraliser.

Preferably the drill bit also comprises reaming members.

According to a third aspect of the present invention there is provided amethod of fixing a hard or super hard wearing material to a drill bitnose made of a soft drillable material, wherein a jet is used to blowgases at very high speeds towards a cast of the nose and particles ofthe hard or superhard wearing material are introduced into the gasstream, wherein the kinetic energy of the procedure is converted tothermal energy which welds the particles to the nose.

According to a fourth aspect of the present invention there is provideda method for fixing a hard or superhard wearing material to a drill bitnose made of a soft drillable material, wherein particles of the hard orsuperhard wearing material are placed within a mould and thereafter thesoft drillable material is poured in molten form into the mould, suchthat on cooling said hard or superhard wearing particles are set insitu.

Alternatively the hard wearing material can be fixed to the nose by astandard technique such as brazing, welding and electroplating.

In order to provide a better understanding of the invention, exampleembodiments of the invention will now be illustrated with reference tothe following Figures in which;

FIG. 1 illustrates a drill bit in accordance with the present invention;

FIG. 2 is an elevated view of the top of the drill bit;

FIG. 3 illustrates an individual cutting member isolated from the drillbit.

FIG. 4 illustrates an elevated view of the top of an alternativeembodiment of a drill bit in accordance with the present invention; and

FIG. 5 illustrates a pre-formed element for attaching to the noseportion of a drill bit.

Referring firstly to FIG. 1, a drill bit generally depicted at 1, iscomprised of a cylindrical body 2, that can be mounted on the lower endof a casing string (not shown) via a thread end connection 3 that canmate with the casing. The drill bit 1 is further comprised of aplurality of cutting members 4 which are fixed to the opposite end ofthe body 2 to the thread end connection 3, namely the nose end 5. Thecutting members 4 extend out from the nose end 5.

The nose 5 and cutting members 4 are constructed from a material such asaluminium, copper or brass alloy which is soft enough to allow theaforementioned nose 5 and members 4 to be drilled through by a secondand subsequent drill bit (not shown). The cutting members 4 aresubstantially covered by a relatively hard material 6 typically being ahard material such as tungsten carbide or a superhard material such asdiamond composite or cubic boron nitride. In the depicted embodiment therelatively hard material 6 is located at the “leading edge” of thecutting member 4. In this respect the “leading edge” refers to the sideof the cutting member 4 which directly contacts the ground or rock uponrotation of the drill bit 1. It is recognised that whilst in thedepicted embodiments the hard wearing material is afforded to theleading edge of one or more cutting members 4 on the drill bit 1, theinvention is not limited to this configuration. For example the hardwearing material may be applied to the nose 5 in an embodiment having nocutting members 4 or may be applied to the whole surface of the cuttingmembers 4.

The relatively hard material 6 may be applied to the cutting members 4or nose 5 as a coating, that is as a layer or film. In one embodiment acontinuous layer of the material 6 may cover the entire surface of thenose 5, or the cutting members 4. Alternatively a non-continuous layerof the material may coat the nose 5 or cutting members 4. In thisinstance, the surface of the nose 5 or cutting members 4 will compriseareas that are not coated. However, upon rotation of the drill bit 1,the cumulative effect of the coated areas will be completecircumferential coverage of the inside diameter of the casing in whichthe drill bit is located.

It is recognised in the present invention that direct application ofsome coatings to the nose material may not be practical. For example,extremely hard tungsten carbide particles cannot be applied to thepreferred nose materials (e.g. aluminium or copper) by lasercarbwelding. This material can be applied to soft nickel, however machiningsaid drill bit 1 entirely from nickel would be unduly expensive.Therefore in an alternative embodiment, a coating of the hard material 6is applied to an intermediate, typically being nickel substrate, whichis then attached to the nose 5 of the drill bit 1. Alternatively thenickel substrate can be attached to the nose 5 prior to coating.

In a further embodiment preformed elements of the hard or superhardmaterial 6 are applied to the nose 5 or cutting members 4 of the drillbit 1 in place of a coating of film. Said preformed elements may bechips, or fragments of the hard material 6. Typically the culmativeeffect of the preformed elements is to cover the surface of the nose 5or the cutting members 4 and so act as a coating thereof. The preformedelements may be directly applied to the nose 5 or cutting members 4 ormay be applied after applying an amenable material either to the nose 5or cutting members 4 or the preformed element itself. The amenablematerial is typically nickel substrate.

The layout of cutting members 4 can be seen more clearly in FIG. 2 whichshows the nose end 5, viewed from above, and in FIG. 3 which shows anindividual cutting member 4. It can be seen in FIG. 3 that the cuttingmeans 6 has teeth formations 10 which allow any “chips” of materialremaining in the well bore to pass through the blade structure.

The nose 5 further comprises flow by areas 7 that allow fluid circulatedwithin the well bore to lubricate the surfaces of the bit 1. The body 2also comprises a stabiliser or centraliser 9 which maintains the drillbit in the centre of the well bore, and reaming members 8, whichfunction to remove any irregularities or obstructions from the wall ofthe bore.

In use, the drill bit 1, is run into a well bore (not shown) from thesurface, typically whilst being rotated. The drill bit 1 pulls a casingstring (not shown) as it is advanced into the newly formed well bore toa predetermined depth. Upon reaching this depth, the casing is cementedto strengthen the lining of the bore. If drilling beyond this firstassembly is required, a second drill bit of a smaller diameter to thefirst is run into the well inside the casing string from the surface.

Upon reaching the first assembly, the new drill bit can drill throughthe soft drillable material of the original drill bit 1 and cuttingmembers 4, and therefore can proceed to a point beyond the depth reachedby the original drill bit 1 within the well bore. The hard or super hardmaterial 6 fixed to the cutting members 4 of the original drill bit 1disintegrate into shavings when drilled. The shavings released into thewell bore when the original bit 1 is drilled through do not obstruct thebore and are therefore not detrimental to the subsequent drillingprocess. In this manner a further section of the bore can be drilledbeyond the previously attained depth without damage to the new drill bitand without needing to retrieve the first assembly from the bore.

When used for drilling through harder formations a thicker section ofthe preformed element will be required. However it will be appreciatedthat in such an instance, said preformed elements would not bedrillable. Thereby in the event that a thicker element is required, saidelement is typically pre-weakened prior to attachment to the nose 5 orcutting members 4. In this manner, the elements will have the attributesof high stiffness whilst drilling but low resistance to fracture whilstbeing drilled. The preformed elements can then be applied directly tothe nose 5 or cutting members 4 by brazing or shrink-fitting or could beattached to an amenable material, typically nickel substrate.

A first method for fixing the hard or superhard material 6 is nowoutlined. A jet is used to blow gases at very high speeds towards a castor block of the cutting member 4 or nose 5, and which is made from thesoft, drillable material. Typically a speed in the region of Mach 2 isused. Very fine particles of the hard or superhard wearing material areintroduced into the gas stream. The resulting kinetic energy isconverted to thermal energy in the particles, and accordingly the heatedparticles “weld” to the leading edge of the cast or block thereforeforming a thin layer or film.

It will be appreciated that the abovedescribed method could be used withparticles of the hard or superhard material, or with intermediatescoated by the hard or super hard material or with preformed elements asdescribed above.

An alternative method for fixing preformed hard or superhard particlesto the cutting members 4 is to place them within a drill mould. Moltendrillable soft material that will eventually become the nose 5 of thedrill bit 1 is then poured into the mould. On cooling the metal providesa drill bit 1 that has the hard or superhard particles set in situ.

The present invention is inherent with significant advantages in thatthe time taken for the drilling operation can be greatly reduced asthere is no need to implement complex and timely retrieval operations torecover apparatus from the bore. As a result the profitable stage ofproduction can be begin much sooner.

A further advantage, is that unlike the drill bits known to the art, thedrill bit of the present invention is drillable by another drill bit andthe risk of damage to the second drill bit is therefore reduced.Furthermore as the cutting means of the cutting members consist of finelayers or cutting elements formed from hard material, they disintegrateinto shavings upon drilling and therefore do not act as an obstructionto any subsequent apparatus that is advanced into the well.

Further modifications and improvements may be incorporated withoutdeparting from the scope of the invention herein intended.

1. A drill bit for drilling with casing in a wellbore, comprising: anose; and cutting members disposed on the nose and made from acombination of a relatively soft base material, a relatively softintermediate material, and a relatively hard material, wherein: the hardmaterial is suitable for cutting earth or rock, the combination ofmaterials is in such proportion and in such arrangement to allow astandard earth drill bit to drill through said drill bit withoutsubstantially damaging said standard earth bit, the cutting members aresubstantially made from the base material, the intermediate material isamenable to the base material and disposed between the hard material andthe base material; the hard material is applied to the cutting membersas preformed elements, the cumulative effect of said preformed elementsis to cover the surface of the cutting members, thereby acting as acoating thereof, and the performed elements are chips or fragments ofthe hard material.
 2. The drill bit of claim 1, wherein the cuttingmembers are disposed proximate to a center of the nose.
 3. The drill bitof claim 1, wherein the nose comprises a flow port.
 4. A drill bit asclaimed in claim 1, wherein the nose is a one piece nose.
 5. A drill bitas claimed in claim 1, further comprising a body, wherein the nose isdisposed on the body and the body is made substantially form therelatively soft material.
 6. A drill bit as claimed in claim 1, whereinthe hard material is tungsten carbide.
 7. A drill bit as claimed inclaim 1, wherein the hard material is diamond composite.
 8. A drill bitas claimed in claim 1, wherein the hard material is cubic boron nitride.9. A drill bit as claimed in claim 1, wherein the base material isaluminum.
 10. A drill bit as claimed in claim 1, wherein the basematerial is copper or brass alloy.
 11. A drill bit as claimed in claim1, having a plurality of base materials.
 12. A drill bit as claimed inclaim 1, having a plurality of hard materials. of the coated areas givescomplete circumferential coverage of the dimensions of the drilled wellbore.
 13. A drill bit as claimed in claim 1, wherein the intermediatematerial is nickel.
 14. A drill bit as claimed in claim 1 wherein theintermediate material is brass.
 15. A drill bit as claimed in claim 1,also comprising a plurality of flow ports to allow fluid bypass andlubrication of the bit.
 16. A drill bit as claimed in claim 1, alsocomprising a stabilizer or centralizer.
 17. A drill bit as claimed inclaim 1, also comprising reaming members.
 18. A drill bit as claimed inclaim 1, wherein the intermediate material and the hard material aredisposed on at least a leading edge or cutting surface of each cuttingmember.
 19. A drill bit for drilling with casing in a well bore,comprising: a nose; and cutting members: disposed on the nose, havingpreformed elements made from a relatively hard material, and made from acombination of a relatively soft base material and a relatively softbonding material, wherein: the hard material is suitable for cuttingearth or rock, the cutting members are made substantially from the basematerial, and the bonding material is disposed on at least a leadingedge or cutting surface of each cutting member between the hard materialand the base material so that, when the nose is drilled through by astandard earth bit, the bonding material will not substantially impedeseparation of the preformed elements, thereby allowing the standardearth bit to drill through the drill bit without substantially damagingthe standard earth bit.
 20. A drill bit as claimed in claim 19, whereinthe bonding material is nickel or brass.
 21. The drill bit of claim 19,wherein the cutting members are disposed proximate to a center of thenose.
 22. A drill bit as claimed in claim 19, wherein the hard materialis tungsten carbide.
 23. A drill bit as claimed in claim 19, wherein thehard material is diamond composite or cubic boron nitride.
 24. A drillbit as claimed in claim 19, wherein the base material is aluminum.
 25. Adrill bit as claimed in claim 19, wherein the base material is copper orbrass alloy.
 26. A drill bit as claimed in claim 19, wherein thepreformed elements have a reinforced structure to aid drilling of hardformations.
 27. A drill bit as claimed in claim 26, wherein thepreformed elements are pre-weakened prior to attachment to the nose inorder to allow fracture of the preformed elements upon drill through bythe standard earth bit.
 28. A drill bit as claimed in claim 19, alsocomprising a stabilizer or centralizer.
 29. A drill bit as claimed inclaim 19, also comprising reaming members.
 30. The drill bit of claim19, wherein the nose comprises a flow port.
 31. A drill bit as claimedin claim 19, wherein the bonding material is nickel.
 32. A drill bit asclaimed in claim 19, further comprising a body, wherein the nose isdisposed on the body and the body is made substantially from the basematerial.
 33. A drill bit for drilling with casing in a wellbore,comprising: a nose; and cutting members disposed on the nose and madefrom a combination of a relatively soft base material, a relatively softintermediate material, and a relatively hard material, wherein: the hardmaterial is suitable for cutting earth or rock, the combination ofmaterials is in such proportion and in such arrangement to allow astandard earth drill bit to drill through said drill bit withoutsubstantially damaging said standard earth bit, the cutting members aresubstantially made from the base material, the intermediate material isamenable to the base material and disposed between the hard material andthe base material; the hard material is applied to the cutting membersas preformed elements, the cumulative effect of said preformed elementsis to cover the surface of the cutting members, thereby acting as acoating thereof, and the preformed elements have a reinforced structureto aid drilling of hard formations.
 34. A drill bit as claimed in claim33, wherein the preformed elements are pre-weakened prior to attachmentto the nose in order to allow fracture of the preformed elements uponchill through by the standard earth bit.
 35. A drill bit as claimed inclaim 33, wherein the cutting members are disposed proximate to a centerof the nose.
 36. A drill bit as claimed in claim 33 wherein the hardmaterial is tungsten carbide, cubic boron nitride, or diamond composite.37. A drill bit as claimed in claim 33, wherein base material isaluminum, copper, or brass alloy.
 38. A drill bit as claimed in claim37, wherein the intermediate material is nickel.